In the recovery of oil from oil-bearing reservoirs, it is usually possible to recover only minor portions of the original oil in place by the so-called primary recovery methods which utilize only the natural forces present in the reservoir. Thus a variety of supplemental recovery techniques have been employed in order to increase the recovery of oil from subterranean reservoirs. The most widely used supplemental recovery technique is waterflooding which involves the injection of water into an oil-bearing reservoir. As the water moves through the reservoir, it acts to displace oil therein to a production system composed of one or more wells through which the oil is recovered.
One difficulty often encountered in waterflooding operations is the relatively poor sweep efficiency of the aqueous displacing medium; that is, the injected displacing medium tends to channel through certain portions of the reservoir as it travels from the injection system to the production system and to bypass other portions. Such poor sweep efficiency or macroscopic displacement efficiency may be due to a number of factors such as differences in the mobilities of the injected displacing liquids and the displaced reservoir oil and permeability variations within the reservoir which encourage preferential flow through some portions of the reservoir at the expense of other portions.
Various techniques have been proposed in order to improve the sweep efficiency of the injected displacing medium and thus avoid premature breakthrough at one or more of the wells comprising the production system. The most widely used procedure involves the addition of thickening agents to the injected displacing medium in order to increase the viscosity thereof and thus decrease its mobility to a value equal to or less than the mobility of the displaced reservoir oil, resulting in a "mobility ratio" of oil to water which is less than or equal to one. Many polymeric thickening agents have been proposed for use in such mobility control applications. One well known class of polymers which may be employed for this purpose is the group of polysaccharides produced by the action of bacteria of the genus Xanthomonas on carbohydrates as disclosed in U.S. Pat. No. 3,305,016 to Lindblom et al. This patent is incorporated herein by reference. As disclosed in this patent, these polysaccharides generally are employed in concentrations within the range of about 0.005-1.0 weight percent, with concentrations within the range of about 0.05-0.25 weight percent normally being preferred. Among the advantages attributed to these polysaccharides by Lindblom et al., are their usefulness in the presence of sodium chloride and other salts and their thermal stability and resistance to adsorption onto rock surfaces within a subterranean reservoir.
Another procedure for improving sweep efficiency involves the use of foams. A foam is a dispersion of a gas in a liquid with an extremely high dispersed phase volume, such that the system can essentially be regarded as a network of interconnected liquid films (J. J. Bikerman, Ind. Chem., 57, 56 [1965]). Foams find a variety of useful applications, including fire fighting (J. M. Perri in "Foams: Theory and Industrial Applications", J. J. Bikerman, Ed., Reinhold Publishing Corp., NY, 1953, Chapter 12), foam fracturing of petroleum reservoirs to improve oil recovery (M. W. Conway and L. R. Norman, U.S. Pat. No. 4,453,596), soil cleanup or detergency (J. J. Bikerman, "Foams"; Springer-Verlag Publishers, NY, 1973, page 254) froth flotation in minerals processing (R. B. Booth in "Foams: Theory and Industrial Applications", J. J. Bikerman, Ed., Reinhold Publishing Corp., NY, 1953, Chapter 13) and mobility control in miscible (D. C. Bond and O. C. Holbrook, U.S. Pat. No. 2,866,507) and thermal oil recovery (W. E. Brigham, O. P. Malito and S. K. Sanyal, " A Field Experiment of Steam Drive with In-Situ Foaming", DOE Report No. DOW/SF/11445-2 [1984]).
Richardson et al. in U.S. Pat. No. Re. 30,935 dated May 18, 1982 disclose initiating production from a gas well which is kept from producing by the hydrostatic pressure of liquid which it contains. Here, an aqueous liquid containing reactants form the nitrogen gas within the well. The gas displaces enough liquid out of the well to lower the hydrostatic pressure to less than the fluid pressure in the adjacent portion of the reservoir. Fluid is thus caused to flow from the reservoir to the well.
None of the methods above mentioned disclose use of a foam generated in-situ within a formation via a decomposable chemical blowing agent. Therefore, what is need is a method whereby a foam can be generated in-situ by a decomposable chemical blowing agent where said foam can be used for fluid diversion or mobility control.